Controlled release polyacrylic acid granules and a process for preparing the same

ABSTRACT

The present invention pertains to a method for forming poly-acrylic acid granules and granules formed therefrom wherein the granules are flowable, have an increased bulk density relative to the as polymerized polyacrylic acids, and a low amount of dust which is generally characterized herein as particles which pass through a 325 mesh screen. The granules formed by the method of the present invention can be used to prepare controlled release tablets, especially controlled release pharmaceutical tablets. The controlled release properties of the tablets formed from granules prepared according to the present invention are unexpectedly better than tablets prepared from granules formed by other known granulation methods.

FIELD OF INVENTION

[0001] The present invention concerns a process for producing granulatedpolyacrylic acid. The polyacrylic polymers are highly swollen in aqueousmedia. The polyacrylic acid granules produced by the process of thepresent invention are useful in controlled release formulations (such aspharmaceutical tablets). The powdered form of polyacrylic acid, whichwas previously used in controlled release applications, created materialhandling problems due to its poor powder flow characteristics, dust, andstatic charges associated with the dust.

BACKGROUND OF THE INVENTION

[0002] Many compounded solids originate or are manufactured as fine,light, and/or loose powders. Such powders often have poor flowcharacteristics and are resistant to blending and dispersion in liquidsdue to clumping and poor wetting. The dust associated with the powderscan exhibit static charge effects. Additional problems includedifficulty in handling and, difficulty in feeding through volumetricmetering equipment. Many such powders have historically been granulatedto vary their particle size distribution in order to improve theircharacteristics. In these applications the larger granules are atemporary state with the granules being easily broken back down into thesmaller powder particles by shear or solvents in the final product.

[0003] Polyacrylic acid resins, which are to be used in applicationsinvolving swelling with aqueous electrolyte solutions, are commonlypolymerized in nonaqueous polymerizations where the insoluble polymercan be isolated as powders. These powders, comprised of aggregated oragglomerated polymer chains, are significantly easier to disperse anddissolve in water than the bulk polymer. However these polyacrylic acidpowders have been noted for their static electricity charge, poor powderflow and some difficult in making dispersions in water since theirintroduction in 1958.

[0004] While some of the difficulties in using and dispersingpolyacrylic acids have been addressed by various improved polyacrylicacids e.g. U.S. Pat. No. 5,349,030 and by adding components to minimizethe effects of ionic charges (e.g. counterions), the problems of productdusting and poor flowability continue to be significant issues,especially with the use of very pure polyacrylic acid resins used in thepharmaceutical industry.

[0005] There are a variety of methods, which have been employed bypowdered material suppliers and users in an attempt to reduce handlingdifficulties of powders. Slugging, hot roll milling, and fluidized bedor wet agglomeration processes are well known processes for convertingpowders to granules. Slugging compresses the powder into large tablets.Hot roll milling uses heat along with pressure to squeeze the powderinto flakes or sheets. In either case, the compacted material is thenreground into particles larger than the original powder grains. Bothslugging and roll milling are relatively slow, low-capacity,energy-intensive processes. Roll milling has the additionaldisadvantages of requiring constant attention by a skilled operator.

[0006] Wet agglomeration techniques involve adding liquid to theoriginal powder to increase the particle sizes and then drying thelarger particles in trays or a fluidized bed. The resulting agglomeratescan be used as is or ground to smaller sizes for specific uses.

[0007] Dry granulation eliminates several problems inherent inconventional processes. Dry granulation of powder material is a two-stepprocess, requiring no heating or wetting (depending on the startingmaterial), in which the powder is first densified (compacted) into solidform, then broken into smaller particles and separated intopredetermined sizes.

[0008] To perform these steps, a granulation system combines severaldifferent kinds of specialized machines (usually in a vertical,gravity-assisted arrangement) to achieve a closed-loop operation. Systemcomponents typically include: a feeding hopper, horizontal and verticalscrews, compaction rollers, a prebreaker, a granulator, sizing/sortingscreens, and a recycling elevator.

[0009] Granulated particles formed by the above processes are moreeasily handled than the powder from which they are formed. However, thegranular particles may be too hard, too soft, too friable or notparticularly suitable, due to the particle size distribution, for theirend use (e.g. tablet forming processes).

[0010] Thus, there is a need to develop a process for preparinggranulated polyacrylic acid suitable for controlled release applicationse.g. pharmaceutical applications, from the polyacrylic acid powder.Desirably the process would produce granules, which retain similarproperties (attributes) during formulation, forming tablets, andreleasing actives from tablets to the powder without the handlingproblems associated with the powder.

SUMMARY OF INVENTION

[0011] The present invention pertains to a method for formingpolyacrylic acid granules and granules formed therefrom wherein thegranules are flowable, have comparable swelling characteristics andprovide comparable tablet properties to powdered polyacrylic acid, haveincreased bulk density, and contain minimal amounts of very smallparticles that can cause dusting and/or static adherence. The granulesfrom this process vary from other granules of similar materials in thatthey retain more of their dissolution and swelling characteristics inboth aqueous solutions in slow release tablets than do prior artpolyacrylic acid granules. The granules formed by the method of thepresent invention can be used to prepare controlled release tablets,especially controlled release pharmaceutical tablets where the granuleshave surprisingly similar characteristics during tablet formation withpowders and form tablets with similar controlled release rates totablets from the harder to handle powders. They can also be used asthickeners; emulsifiers and suspending agents in water basedformulations based on other polar solvents.

[0012] Thus, a first advantage of the present invention is thatpolyacrylic acid powder is formulated into a granular product withbetter dry flow characteristics facilitating metering and mixingoperations.

[0013] An additional advantage is the production of a granularpolyacrylic acid having better control over particle size, higher bulkdensity to minimize packaging, and lower static adherence compared tounprocessed powdered polyacrylic acid.

[0014] A further advantage is that the granular polyacrylic acidproduced in accordance with the present invention has relatively lowdusting compared to the powder form of polyacrylic acid.

[0015] A still further advantage of the granular polyacrylic acid of thepresent invention is that it results in the unexpectedly bettercontrolled release of various active material from tablets formed fromthe granules than from tablets formed from granules produced by othergranulation processes.

[0016] The term polyacrylic acid is used to include various homopolymersand copolymers wherein at least 50 or 75 mole percent of the repeatingunits have pendant carboxylic acid groups or anhydrides of dicarboxylicacid groups. While acrylic acid is the most common primary monomer usedto form polyacrylic acid the term is not limited thereto but includesgenerally all α-β unsaturated monomers with carboxylic pendant groups oranhydrides of dicarboxylic acids as described in U.S. Pat. No.5,349,030.

[0017] Other advantages and benefits of the invention will becomeapparent to those skilled in the art upon a reading and understanding ofthe following detailed description of the preferred embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The Figure shows one example of a compaction/granulation systemwith a recycle mechanism.

DETAILED DESCRIPTION

[0019] In accordance with the practice of the present invention, a drygranulation apparatus A is provided as shown in the Figure. Variablessuch as the compaction pressure, roll speeds, attrition device andoperation speed, and screening operations are used to control theparticle densification and particle size distribution. These propertiescontrol the dissolution behavior of the polyacrylic acid when exposed towater or electrolyte solutions and its effectiveness as an additive intablet formulations and controlled release applications.

[0020] Referring now to the FIGURE, the dry granulator A is providedwith an original powder feed 10 which feeds powdered polyacrylic acidinto a lower hopper 12. The powdered acrylic acid in lower hopper 12 isthen fed through feed channel 14 into an upper hopper 16. The upperhopper 16 collects the virgin powdered polyacrylic acid and recycledpowder which does not meet quality controlled sizing parameters. Thepowdered acrylic acid in the upper hopper is then initially fed into thegranulation system via a horizontal feed screw 18. The rate of rotationof the horizontal feed screw 18 can be adjusted to permit continuousflow of the powdered polyacrylic acid into the granulation systemwithout clogging. Next, a vertical screw 20 precompresses and deaeratesthe powered polyacrylic acid before feeding it into compaction rollers22. Pressure is applied to compaction rollers 22 via a hydraulicactuator 24. The compaction rollers rotate in opposite directions sothat powdered material fed from above will be pulled between therollers, compressed and dropped into a prebreak mechanism 26 below. Theprebreak mechanism 26 provides an initial breakup of the compressedpolyacrylic acid into chips and flakes, which drop into attritor 28. Theattritor 28 breaks up the compressed polyacrylic acid into desiredparticle sizes in conjunction with screen 30. Granulated polyacrylicacid falls into a screening system 32 wherein particles are separatedvia various sieves 34, the final product having the desired particlesizes being deposited into finished product hopper 36. The oversized andundersized particles 38 are processed via a recycle feed mechanism 40back into feed channel 14, 42 to be reprocessed through the system.

[0021] Various powdered polyacrylic acids, or mixtures of polyacrylicacids, may be granulated according to the process of the presentinvention wherein the resulting granulated polyacrylic acid has enhancedhandling and performance properties compared to the powder. Thegranulated polyacrylic acid prepared in accordance with the methoddescribed herein, when formulated into tablets retains an ability toslow down the release rate of an active material, compared to tabletsformed from granules prepared by other known granulation processes. Thegranules also maintain more of their ability to thicken, emulsify, andsuspend in water based formulations and formulations based on otherpolar solvents than prior art granules.

[0022] Polymeric powders which may be formed into granules that haveimproved handling, while retaining thickening and controlled releaseproperties, include various acrylic acid homopolymers, copolymers, andinterpolymers having a bulk density below about 0.3 g/cc. The termpolyacrylic acid or acrylic acid polymers is used to encompass a varietyof polymers having high percentages of polymerizable monomers thereinwith pendant carboxylic acid groups or anhydrides of polycarboxylicacid. These are described in more detail in U.S. Pat. Nos. 2,798,053;3,915,921; 4,267,103; 5,288,814; and 5,349,030 hereby incorporated byreference. The term polyacrylic acid is used to include varioushomopolymers, copolymers, and interpolymers, wherein at least 50 or 75mole percent of the repeating units have pendant carboxylic acid groupsor anhydrides of dicarboxylic acid groups. While acrylic acid is themost common primary monomer used to form polyacrylic acid the term isnot limited thereto but includes generally all α-β unsaturated monomerswith carboxylic pendant groups or anhydrides of dicarboxylic acids asdescribed in U.S. Pat. No. 5,349,030. The term consisting essentially ofanhydrous polyacrylic acid will be used to exclude more than 3 weightpercent water and to exclude more than 0.2 mole percent multivalentmetal cations based on the moles of carboxylic acid. Desirably, theamount of water is less than 1 or 2 weight percent. Desirably, theamount of multivalent metal cations is less than 0.1 mole percent andpreferably less than 0.01 mole percent.

[0023] In particular, the process according to the present inventions isuseful for granulating various powdered polycarboxylic acids includingcross-linked polyacrylic acids. Specific types of cross-linkedpolyacrylic acids include Carbopol® 971P (polymerized in ethyl-acetateand partially neutralized with potassium); copolymers of acrylic acidand alkyl acrylates; copolymers of acrylic acid and alkyl vinyl ethers;copolymers of ethylene and maleic anhydride; and copolymers of maleicanhydride and alkyl vinyl ethers. An approved polyacrylic acid forpharmaceutical applications, described in a carbomer monograph in theU.S. Pharmocopia 23 NR 18, is a polyacrylic acid crosslinked withpolyalkenyl ethers. The polymeric agents useable in the presentinvention are typically polymerized by precipitation polymerization in anon-aqueous medium and subsequently dried to strip off the solvent. Theacrylic polymers typically have a flow index of above 30, apparently dueto their low bulk density and electrostatic charge.

[0024] The acrylic polymers of interest when dispersed in water andneutralized to a pH of 7 at a concentration of 10 g/L generally canimpart a viscosity of at least 500 centipoise and more desirably atleast 2000 centipoise to the water solution as measured by a Brookfieldviscometer using 20 rpm at 25° C. and selecting a spindle resulting in atorque reading between 10 and 90% of full scale.

[0025] The improved handling properties of the granules prepared inaccordance with the present invention are reflected by improvements overthe powdered form of polyacrylic acid in areas such as powder flow rate,bulk density, percentage of fines (i.e. particles less than 325 U.S.Standard screen size), static adherence and total dust.

[0026] The granulated product desirably retains the at least 70, 80 or90% of the thickening capacity of the original fine powder whendispersed in water and neutralized to a pH of 7 at a concentration of 10g/L. Thus the viscosity of such a solution is desirably at least 350,400, or 450 centipoise and more desirably at least 1400, 1600 or 1800centipoise.

[0027] With respect to powder flow rate, the granules according to thepresent invention may have a flow index value of less than or equal to25, desirably less than or equal to 20, and preferably less than orequal to 15. The flow index is measure by the Flodex™ equipment, whichcomprises a 35-45 mm diameter tube approximately 8-10 cm long. Bottomcaps with incrementally larger diameter apertures are used in theapparatus until an aperture is found of sufficient diameter that thecontents of the tube are substantially emptied from the tube when theaperture is unblocked by the operator. A flow index value is assignedequal to the diameter of the aperture used in mm through which thematerial flows easily. If the aperture is too small then bridging overoccurs with a substantial amount of the tube contents being retained inthe tube.

[0028] The bulk density of the granules is measured according to atypical bulk density method for powders. A 30-100 mL cup is used whichcan be lightly tapped one time after filling. The powder is dropped froma powder funnel which discharges about 4 to 8 cm above the rim of thecup. The excess material which accumulates above the rim of the cup canbe removed by scraping with a spatula and the weight of the contentsdetermined. The bulk density is the weight of the contents divided bytheir volume. A tap density can also be determined using a 100 mLgraduated cylinder instead of a cup. The powder is discharged from thebottom of a powder funnel as set forth above. A tap density apparatussuch as a J. Engelsmann A-G Tap Density Apparatus is used to tap thecylinder and contents 1000 times. The volume and weight of the powderafter tapping is recorded and the density is calculated as the weightdivided by the volume.

[0029] Due to the propensity of very small particles to cause dusting,it is desirable to screen the granules to remove and recycle thosegranules which pass through a 325 U.S. Standard mesh screen. This is notto say that particles smaller than a 325 mesh screen are dust but ratherthat this size fraction includes more dust and/or carries more dust withit into other steps. Desirably the amount of granules that pass throughsaid 325 mesh screen are less than 10 weight percent of the totalgranules, more desirably less than 5 weight percent, and preferably lessthan 2 weight percent of the granulated product after screening. Theamount of granules passing through a 325 mesh screen can be determinedby screening the granules until the weight of the material passingthrough the 325 mesh screen appears to be constant. If a screen analysison the polyacrylic powder (before granulation) is desired, small samplesizes or air filtration techniques are recommended due to thesubstantial amount of very small particles in the powder and staticcharge problems that occur during screening.

[0030] Static charging for polyacrylic acid is generally visuallydetermined. Powder samples in bags will exhibit a strong tendency fordust to adhere to the bag and any equipment and/or the operator. Samplesof polyacrylic acid powder in glass and plastic jars (generallynonconductive) will exhibit large amounts of dust adhered by staticelectricity to the walls of the jar above the samples. Static chargeddust particles will appear to exit the glass jar as a smoke due tostatic repulsion combined with Browman particle diffusion.

[0031] In order to achieve production of polyacrylic acid granules,which possess both the improved handling properties over the powder andretain acceptable tablet formation and controlled release propertiescompared to the powder, a number of adjustable parameters must becontrolled. These parameters include horizontal feed screw rate ofrotation, vertical screw rotation speed, pressure applied to compactionrolls, speed of compaction rolls, attritor configuration and speed, andscreen size.

[0032] The speeds of the horizontal and vertical screws should be set tofeed powder to the compaction rollers at a rate just fast enough tocause a slight separation (about 0.01 to about 0.2 or 0.5 inches, moredesirably from about 0.02 to about 0.07 or 0.2 inch gap) between therollers.

[0033] Pressure is applied to the compaction rollers via the hydraulicactuator or other compaction device to produce a compacted materialhaving a density of about 0.3 g/cc to about 1.5 g/cc. Preferably, thedensity of the compacted material is from about 0.9 g/cc to about 1.1g/cc. These densities form strong enough aggregates and/or agglomeratesthat the amounts of undersized particles can be reduced without removingso much of the voids, cracks, and crevices (void volume) within theaggregates and agglomerates to prevent them uniformly swelling in wateror electrolyte solutions. The compaction rolls may have circumferientialcorrugations, pocket indentations or corrugations in the axial directionacross the width of the roll. Applicants define the pressure via theresult due to the complexity of specifying a compaction pressure appliedfrom a curved surface to a powder.

[0034] Densification obviously is the result of compacting theaggregates and/or agglomerates (particles) present in the powder intolarger particles. This reduces the void volume within the particles. Itis believed that the void volume, to the extent that it is open to thesurface of the particles, is a pathway for water or electrolytesolutions to enter each particle uniformly swelling the polyacrylic acidtherein. Thus densification usually makes the interior of the particlesless accessible to water or electrolyte solutions.

[0035] Increased compaction also results in more interpolymerpenetration between the surface polymers on aggregates and/oragglomerates, which can slow dissolution times of a particle due to theneed for the interpenetrated polymers to separate and due to thepossibility that the interpenetrated polymers may remain entangled andnot be able to separate. It is to be noted that if the polyacrylic acidis over-densified then the resulting granules will only swell with wateror electrolyte on their surfaces. This results in occlusions ofnonswollen polymer (occluded polymer) within some or all granules.

[0036] The occluded (non-swellable) polyacrylic acid is not available tomodify the viscosity of liquid solutions and is not available to controlrelease rates in a tablet. Therefore there is an inverse relationshipbetween the amount of occluded polyacrylic acid and the thickening andrelease controlling properties of the polyacrylic acid.

[0037] The compaction roller speed is set to maximize productivitywithout exceeding the horsepower limitation of the compaction equipment.Slower roller speeds allow the polyacrylic acid more time to flow andaccommodate the stresses uniformly throughout the thickness of thecompressed samples. Faster roller speeds may force the polyacrylic acidin direct contact with the roller surface to do most of theaccommodation.

[0038] The speed and configuration of the attritor are chosen to provideoptimal particle size distributions for a particular application.Smaller particles, such as those sized between the opening of a 100 and200 mesh screen are desirable as they maximize the number of particlesand total surface area. These properties are important, as smallerpolyacrylic acid particles tend to form a tablet with better integrityand slower release rates for active material. Increases in the number ofsmaller particles decreases bulk density and decrease powder flowcharacteristics. It has also been observed that smaller particles formtablets with better tablet integrity in the dissolution tests. Largerparticles, e.g. those sized between a 20 and 80 mesh screen, maximizebulk density and flow characteristics but contribute less to tabletformation and slow release rates. In most embodiments it is desirable tominimize generation of granules smaller than 325 mesh, more desirableless than 200 mesh (U.S. Standard) due to their contribution to dust.

[0039] Screen size is about 5 mesh to about 325 mesh (U.S. Standard);more desirably from about 20 to about 250, and preferably, screen sizeis from about 40 mesh to about 200 mesh. Thus, granules having aparticle size of less than about 5 mesh (passing through 5 mesh) butgreater than about 325 mesh (retained on 325 mesh) will be discharged asproduct. Particles which have sizes outside these parameters (oversizedand undersized (fines)) will desirably be recycled back into the systemif present in a significant amount.

[0040] Vacuum deaeration may be used to reduce air from becoming trappedin the powder prior to compaction. The vacuum may be adjusted to be fromabout 0.5 in. Hg. to about 30 in. Hg. Preferably 5 to 20. Desirably thisvacuum is applied around the compaction rolls and optionally within thevertical and/or horizontal screw feeds. If alternative compaction orpowder conveyance means are used they could include vacuum deaeration.Entrained air in the material from the initial compaction tends toexpand uncontrollably as the compacted material comes out of thecompaction rolls and fracture the compacted material.

[0041] The controlled release tablet formulations of the presentinvention include granulated polyacrylic acid prepared in accordancewith the process of the invention. Amounts of polyacrylic acid used intablet formulations are preferably from about 5 or 10% w/w to about 50%w/w. The polyacrylic acid aids in tablet formation and tablet integrity.During controlled release applications the polyacrylic acid can swellwhich limits the porosity of the tablet (or application device) byrestricting the flow of the electrolyte solution into and out of thetablet. Desirably the tablets made according to this disclosure have arelease rate of from about 0.6 to about 24 hours or more forpharmaceutically active materials. Longer release rates are availablefor non-pharmaceutical applications where the longer release rates maybe desirable.

[0042] Other conventional tableting adjuvants, includingpharmaceutically acceptable tableting adjuvants, can be included in thetablet formulations. Such adjuvants include fillers, excipients,compression aids, binders, flavorings, coating agents, etc.

[0043] Various active materials, e.g. pharmaceuticals, may be formulatedinto the controlled release tablet formulations. Other active materialsinclude biocides, disinfectants, stimulants, moisturizers, aromas,scents, chemicals (e.g. chlorine), proteins, etc which are beneficiallyapplied from a table or gelled or thickened liquid formulation.Typically, pharmaceuticals dosages are designed to be administered inspecific amounts over a broad time range to avoid toxicity problems,thus the need for controlled release formulations. Pharmaceutical caninclude pain relievers, stimulants, muscle relaxants, antibiotics, painblockers, and a variety of other medications. Theophylline, for example,is one such agent, which is generally formulated in a controlled releasetablet composition. Other pharmaceutical agents typically or desirablyused in controlled release form are within the scope of acceptablepharmaceutical agents useable in the present invention's formulations.

PREPARATION EXAMPLES

[0044] The following examples illustrate the processes for preparingpolyacrylic acid granules, which possess the desired handling andcontrolled release properties.

PREPARATION EXAMPLES 1 AND 2

[0045] The following examples utilized a Fitzpatrick Model 4L×10DChilsonator and DKAS012 FitzMill system. This equipment is illustratedin FIG. 1. The Fitzpatrick Company has a compaction division inElmhurst, Ill., which sells this type of equipment. Another supplier ofsimilar equipment is Alexanderwerk based in Germany and having a salesoffice in New Jersey. The Chilsonator used two 4″ long rolls havingdiameters of 10″. Vacuum was applied in the area of the vertical screw.The material granulated was Carbopol® 971P, a lightly crosslinkedpolyacrylic acid powder. TABLE I Example 1 Example 2 Feed (lbs/hr.)  360 390 Roll Pressure (psig)  800 1000 Roll Speed (RPM)  12  12 Vacuum (in.Hg.)   7   7 Granulator Speed (RPM) 1250 1250 Screen size/type0.079/Rasping .079/Rasping Sieve Size (mesh) 10-84 10-84 % Product  82 85 wt. % Overs/wt. % Fines 1.8/16  1.6/14 

[0046] TABLE Ia Example 1 Example 2 Powder (From Table I) (From Table I)T₇₀SGF* 482 310 244 (minutes T₇₀SIF* 627 347 274 (minutes)

[0047] Tables I and Ia show that drug release time can be adjusted bymanipulating roll compaction pressure. The tablet from Table Ia releaserate tests was formulated with a similar recipe to Table III, andcompacted with sufficient pressure to result in a tablet with a hardnessof 9-11 kilopounds using a standard U.S.P. crushing strength tester.TABLE Ib Viscosities of Aqueous Dispersions at Various ResinConcentrations (Neutralized to about pH 7.5 with NaOH) Example 1 Example2 Powder (from Table I) (From Table I) 0.2% Resin 3250 2930 2810 0.5%Resin 6050 5750 5700 1.0% Resin 9850 9300 9300 1.0% Resin + 3070 27002680 1.0% NaCl

[0048] Tables I and Ib show how thickening ability decreases onlyslightly with increasing compaction pressure. However, it should benoted that the gel surface may appear rougher with increasing compactionpressure.

Formulation Examples

[0049] The following examples illustrate the physical characteristics ofgranules produced according to the present invention. The samples wereprepared using a Fitzpatrick IR-520 Chilsonator roll compactor and a M5AFitzmill attritor. Carbopol®971P was used in the following examples.TABLE II Formulation Roll Speed/ Flow Flow Example # Pressure (RPM) −20mesh* 20-80* 1     5/1,000 22 18 2   10/700 32 24 3  — 34 n/a(Control-powder) 4** n/a 22 22 (comparative Example)

[0050] The following Examples illustrate pharmaceutical tabletformulations comprising theophylline. Examples 1 and 2 utilize Carbopolgranules from Table II above. Comparative examples include powderedpolyacrylic acid and polyacrylic acid granules produced by fluidized bedgranulation. All amounts used in % w/w. TABLE III Ex. 3 Ex. 1 Ex. 2(powder) Ex. 4 Theophylline 33.3 33.3 33.3 33.3 Anhydrous Lactose 45.745.7 45.7 45.7 Carbopol ®971P 20.0 20.0 20.0 20.0 (as is or granulated)Cab-O-Sil 0.5 0.5 0.5 0.5 Magnesium Stearate 0.5 0.5 0.5 0.5

[0051] Table IV, below, shows properties of powder mixtures and tabletsformed from granules prepared according to the present inventioncompared to powder mixtures and tablets formed from either powderedpolyacrylic acid (Ex. 3) or granules produced via the fluidized bedtechnique (Ex. 4). TABLE IV Ex. 3 Ex. 4* Ex. 1 Ex. 2 (powder)(comparative) Flodex 32 26 32 >32 (flow index) (before tableting)Compressibility 22.9 18.8 21.8 28.5 Index (before tabletting) T₇₀**  100/573.58 162/623  466/1006 62/66 SGF/SIF*** T₉₀** 122/663 210/725 673/1343         71.6/(<90) SGF/SIF*** (minutes

[0052] Table IV shows that the flowability (flow-index) of the tabletingpowder mixture prepared from various granular forms of polyacrylic acidis not fundamentally related to the drug release performance of thegranules. The compressibility index is 100 times the difference betweenthe tap density and bulk density divided by the tap density. In freeflowing powders, the compressibility index is less than 15% while valuesabove 25% indicate poor flow characteristics.

[0053] The following Tables V-VII illustrate the dramatic effect ofcompression pressure during compaction of the polyacrylic acid granuleson the properties of the tablet blends when using the polyacrylic acidas a 10 weight percent ingredient. The polyacrylic acid of Example 5 wascompacted under a pressure of 10 bar on an Alexanderwerk granulatingmachine, Example 6 was compacted under a pressure of 30 bar, and Example7 was compacted under a pressure of 60 bar. TABLE V Composition Ex. 5Ex. 6 Ex. 7 Theophylline 32.9 g 32.9 32.9 Anhydrous lactose 55.7 55.755.7 Polyacrylic acid 10 10 10 Compaction pressure for polyac- 10 30 60rylic acid (bar) Cabosil (fumed silica) 0.4 0.4 0.4 Magnesium stearate1.0 1.0 1.0

[0054] TABLE VI Properties of Tablet Blend Properties Ex. 5 Ex. 6 Ex. 7Bulk density .0566 0.404 0.476 Tap Density 0.765 0.475 0.560 HausnerRatio 1.352 1.175 1.176 Compressibility Index % 26.01 14.95 15.00

[0055] The tablet blends in Table V were formed in a 0.375-inch diameterdie with a blend loading of 300 mg for each of Examples 5-7. The forceused for Examples 5 was 300 lbs, that for Example 6 was 364 lbs, andthat for Examples 7 was 367 lbs. These values were calculated based onthe Hausner Ratio and the Compressibility Index of the tablet blend. TheHausner ratio is the tap density divided by the bulk density. It is tobe noted that the hardness of the tablets from Examples 5-7 were 8.7,8.8, and 8.4 lbs indicating that Examples 6 and 7 were not compressedinto harder tablets than Example 5. TABLE VII Properties of Tablet Ex. 5Ex. 6 Ex. 7 Release in SGF T20 60 52 39 T50 279 152 70 T70 445 196 81T90 764 316 92 Release in SIF T20 174 184 153 T50 702 592 460 T70 1133828 627 T90 — 1173 712 Dissolution Time (min) 34.9 33.5 36.0 Tabletthickness (inch) 0.1748 0.1728 0.1755

[0056] The above Table VI illustrates what a dramatic effect 10 weightpercent of polyacrylic acid, granulated under different conditions, canhave on the properties of blends used to make tablets and Table VIIillustrates the dramatic effect on the release rate of theophylline. Asis well known to the pharmaceutical industry, theophylline is a veryeffective medication, but it can be toxic if released in concentrationsabove the pharmaceutically effective amounts. Therefore uniform andcontrolled safe dosages of theophylline are critical in preparingeffective tablets. In Table VI the blend before tablet making from thepolyacrylic acid compacted under the lowest compaction pressure resultedin the densest blend with the highest compressibility (facilitatingtablet formation at lower pressures). When these blends were compressedinto tablets the compaction pressures used to form granules ofpolyacrylic acid had little effect on the disintegration times. Therelease time of theophylline by the tablets was dramatically decreasedby increasing compaction roll pressure.

Results

[0057] As can be seen from the tables above, granules produced inaccordance with the present invention have enhanced flowability comparedto the control powder (Table II). Additionally, Table II shows theimportance of screening out fines to achieve increased flowability.

[0058] In addition to enhanced flowability, tablets prepared fromgranules of polyacrylic acid made in accordance with the process of thepresent invention possess enhanced (slowed down) controlled releaseproperties over granules of polyacrylic acid prepared by other knowngranulation processes (i.e., fluidized bed). While the controlledrelease properties of tablets prepared from granulated polyacrylic acidaccording to the present invention are not quite as slow as tabletsprepared from powdered polyacrylic acid, the undesirable handlingproperties of prior art powders are avoided as the granules haveimproved flowability, lower static adherence and lower dust compared tothe powdered polyacrylic acid itself. These major advantages inpretableting handling characteristics more than compensate for thesomewhat lowered thickening efficiency or slight changes in thecontrolled release properties.

[0059] While in accordance with the patent statutes the best mode andpreferred embodiment has been set forth, the scope of the invention isnot limited thereto, but rather by the scope of the attached

What is claimed is:
 1. A process for granulating polyacrylic acid suchthat the granulated polyacrylic acid has the following properties: (i) aflow index of≦25, (ii) a bulk density of at least 0.35 g/cc, and (ii)less than 5 wt. % particles are fine enough to pass through a U.S.Standard 325 mesh screen, said process comprising: (a) delivering a finepowder consisting essentially of anhydrous polyacrylic acid to acompaction device; (b) compacting said polyacrylic acid into largeragglomerates and/or aggregates, (c) fracturing said agglomerates and/oraggregates into smaller granules; (d) optionally screening said smallergranules to obtain the desired particle size range by removing orrecycling in said process oversized and/or undersized granules, saidpolyacrylic acid being a polymer of one or more monomers characterizedby having at least 50 mole percent repeating units having a carboxylicacid group and/or an anhydride of a dicarboxylic acid and when dispersedin water and neutralized to a pH of 7 at a concentration of 10 g/Limparting a viscosity of at least 500 centipoise to said water.
 2. Theprocess of claim 1 wherein said compacting of said polyacrylic acid isachieved by the use of compaction rollers.
 3. The method of claim 2wherein said compacting rollers are adjusted to a separation between theroller of from about 0.01 to about 0.5 inches.
 4. The method of claim 3,wherein the pressure on said rollers is sufficient to form a coherentstrip from the compaction rollers.
 5. The method of claim 1 wherein thepolyacrylic acid is a cross linked polyacrylic acid.
 6. The method ofclaim 1 wherein the fine powder, optionally with undersized and/oroversized granules, is delivered to said compaction device via one ormore vertical and/or horizontal screws.
 7. The method of claim 1 whereinthe granules produced have an average particle size of between 5 and 325U.S. Standard mesh screen.
 8. A granular polyacrylic acid productproduced by the process of claim 1 wherein the granular product has thefollowing properties: (i) a flow index of≦25, (ii) a bulk density of atleast 0.35 g/cc, (iii) less than 5 wt. % particles are fine enough topass through a U.S. Standard 325 mesh screen, and, (iv) said granularpolyacrylic acid being a polymer of one or more monomers characterizedby having at least 75 mole percent repeating units having a carboxylicacid group or an anhydride of dicarboxylic acid and when dispersed inwater and neutralized to a pH of 7 at a concentration of 10 g/Limparting a viscosity of at least 400 centipoise to said water.
 9. Agranular polyacrylic acid product according to claim 8 incorporated in atablet.
 10. A method for providing polyacrylic acid for controlledrelease applications including the steps of polymerizing acrylic acidwith one or more other monomers in a nonaqueous media where thepolyacrylic polymer is insoluble in the polymerization media and whereinthe recovered polymer, when dispersed in water and neutralized to a pHof 7 at a concentration of 10 g/L, imparts a viscosity of at least 500centipoise to the water, the improvement comprising; (a) delivering afine powder consisting essentially of anhydrous polyacrylic acid to acompaction device; (b) compacting said polyacrylic acid into largeragglomerates and/or aggregates, (c) fracturing said agglomerates and/oraggregates into smaller granules; (d) optionally screening said smallergranules to obtain the desired particle size range by removing orrecycling in said process oversized and/or undersized granules.
 11. Theprocess of claim 10 wherein said compacting of said polyacrylic acid isachieved by the use of compaction rollers.
 12. The method of claim 11wherein said compacting rollers are adjusted to a separation between theroller of from about 0.01 to about 0.5 inches.
 13. The method of claim12, wherein the pressure on said rollers is sufficient to form acoherent strip from the compaction rollers.
 14. The method of claim 10wherein the polyacrylic acid is a cross linked polyacrylic acid.
 15. Themethod of claim 10 wherein the fine powder, optionally with undersizedgranules, is delivered to said compaction device via one or morevertical and/or horizontal screws.
 16. The method of claim 10 whereinthe granules produced have an average particle size of between 5 and 325U.S. Standard mesh screen.
 17. In a method for making a controlledrelease tablet including the steps of 1) formulating a tablet blend fromi) a material to be released in a controlled manner, ii) polyacrylicacid in a readily water swellable form, and iii) conventional tabletformation adjuvants, and 2) forming and compressing the tablet blendinto a tablet, the improvement comprising a step prior to formulatingsaid tablet blend of converting said polyacrylic acid in a readily waterswellable form a fine powder to a granular form that is also readilywater swellable by (a) delivering a fine powder consisting essentiallyof anhydrous polyacrylic acid to a compaction device; (b) compactingsaid polyacrylic acid into larger agglomerates and/or aggregates, (c)fracturing said agglomerates and/or aggregates into smaller granules;(d) optionally screening said smaller granules to obtain the desiredparticle size range by removing or recycling in said process oversizedand/or undersized granules, said polyacrylic acid being a polymer of oneor more monomers characterized by having at least 50 mole percentrepeating units having a carboxylic acid group and/or an anhydride ofdicarboxylic acid and wherein said polyacrylic acid when dispersed inwater and neutralized to a pH of 7 at a concentration of 10 g/L impartsa viscosity of at least 500 centipoise to said water.